Observation of the Beam-Beam Limit in CESR

CESR has produced e+ e- collisions for high energy physics in the very productive T region (4.7 to 5.7 GeV per beam) since the fall of 1979. The peak luminosity recorded during physics data taking over that period is shown in Fig. 1. The dramatic increase in the luminosity has resulted from the reduction of ßy* from 11 cm to 3 cm, an increase in σx *, and increases in the vertical aperture. Furthe...